The present invention relates to a packet transmission device that transmits packets for measuring a bandwidth that is available when data communication is performed via a network, a packet transmission method and a computer program product stored on a non-transitory computer-readable medium.
Communication devices are known that transmit and receive data via a network such as the Internet. It is preferable for the communication devices to transmit and receive data at a transmission rate that is appropriate for an available bandwidth for the communication devices. The available bandwidth for the communication devices varies depending on conditions including a region, a provider and a time zone. Given this, in order to control the transmission rate in accordance with a variable available bandwidth, a packet transmission method has been proposed that determines whether or not a current transmission rate is appropriate for the available bandwidth. With the method, packets for the above determination (each of these packets is hereinafter referred to as a “determination packet”) are transmitted and received in a communication system, and the available bandwidth and the current transmission rate are compared.
More specifically, a transmission-side communication device transmits the determination packets each including, as transmission time, time information that enables acquisition of a transmission interval of the determination packets. When a receiving-side communication device receives each of the determination packets transmitted from the transmission-side communication device, the receiving-side communication device acquires a reception time. The receiving-side communication device calculates a reception interval using the reception times, and calculates the transmission interval using the transmission times. Further, the receiving-side communication device compares a difference between the reception interval and the transmission interval with a threshold value, and thereby determines whether or not the current transmission rate is appropriate for the available bandwidth.
Further, a bandwidth measurement method has been proposed to measure a variable available bandwidth. In this bandwidth measurement method, at timings to measure the available bandwidth, a transmission-side communication device continuously transmits a plurality of packets while changing the transmission intervals. The receiving-side communication device records reception intervals of the packets. The receiving-side communication device calculates differences between the transmission intervals and the corresponding reception intervals, and measures a currently available bandwidth based on a change tendency of the calculated plurality of difference values.